[geekwithvaguememoryofphysics] The fluorescent yellow or orange of hi-viz etc can appear to glow as if more light is being reflected from it compared a similar coloured surface. Fluorescence occurs when UV light is converted to a longer wavelength so it becomes visible. Add that to the normally reflected light and it appears to glow.

. . . For fluorescence to work requires UV. Usually from sunlight, sometimes from 'blacklight' - see raves.

Unless anyone knows better, there isn't much UV from streetlamps or headlights.

And ubergeek: the actual colour* doesn't matter - that's how 'whiter than white' washing powder works, it adds a chemical which fluoresces. Unfortunately, these chemicals 'wear out', leaving a residue whuch makes the clothes look grey. Ironically, hi-viz clothing needs to be washed very carefully and can only be cleaned a few times (see the label).

* BS CE 200471 (or whatever the current one is) allows orange yellow and red, within defined colourspace. Rail workers have to wear orange, from a tighter range.

I wondered about "particularly since low-beam headlamps will not effectively illuminate retro-reflective material on a jacket" given that low beams effectively illuminate road signs - is this point more to do with what drivers are or aren't looking for, and maybe what they perceive, rather than anything else?

ancient wrote:With correctly functioning headlights (which I have) and attention to what is in my planned path, I can see completely unlit objects in dark matt colours in good time to not drive into them.

It's all very well but, when you throw an oncoming motor vehicle into the mix, then it's bloody hard to see those pedestrians unless there is some odd light movement to catch the eye.

ancient wrote:With correctly functioning headlights (which I have) and attention to what is in my planned path, I can see completely unlit objects in dark matt colours in good time to not drive into them.

It's all very well but, when you throw an oncoming motor vehicle into the mix, then it's bloody hard to see those pedestrians unless there is some odd light movement to catch the eye.

Which is why if dazzled by oncoming, I slow down or stop. I don't assume anything behind the dazzle is hi-viz or that if it were, that would help. Twice recently this has saved the life of vulnerable road users, one of whom was wearing white jumber and gloves and HiViz reflective waistcoat and was completely invisible until after I stopped. I gave her a lift into town (about 10 miles) and she was convinced that I must have seen her 'safety' vest. I didn't, just blackness behind the bus' headlights.HiViz doesn't compete against dazzle and adding more lights just creates worse dazzle. We are already beyond the place where vehicles (motorised and otherwise) were putting out enough light to 'see and be seen'. There is now so much light on the roads that police accident investigators are letting drivers off because there are so many lights that it is confusing!

ancient wrote: By "seen earlier" I meant that they are processed as part of the scene. That is what I was trying to get at when comparing them to road furniture. HiViz does look like road signs - especially when not particularly paying attention (i.e. not 'wondering what that is' for everything in the path of the vehicle). Road signs need no particular avoidance plan, the way something in the road would, so HiViz may get dismissed as 'no threat - nothing to do'. Looking like road furniture in the distance is not necessarily a way to be "conspicuous", although more light does reach the drivers' eyes from the HiViz - so they are 'seen'.

Gareth wrote: I wondered about "particularly since low-beam headlamps will not effectively illuminate retro-reflective material on a jacket" given that low beams effectively illuminate road signs - is this point more to do with what drivers are or aren't looking for, and maybe what they perceive, rather than anything else?

Replying to these two together as I think they're addressing the same area of how we identify what's ahead.

From one of my old blog posts:

So why am I bringing Road Safety Dog out for another walk along the highways? Well, he provides a very simple way of explaining how 'visibility' differs from 'conspicuity', and the varying types of conspicuity which exist.

So, what is 'visibility'? Quite simply, it means something is visible, it's not hidden. Inside his kennel RSD is probably hidden from your view, so he's not visible. When he walks out to bask in the Sun he then becomes visible.

But is he 'conspicuous'? Well, possibly. But there are three levels of conspicuity:•Search conspicuity•Attention conspicuity•Cognitive conspicuity

RSD can do all of these! In doing so, he may help you understand how you may - or may not - be seen when out on the road.

If you walk into a room, and just glance around, you may miss Road Safety Dog because he’s asleep in the far corner. But if I ask you to look for a dog you’re more likely to see him. That, perhaps unsurprisingly, is called ‘search conspicuity’.

However, I didn’t ask you to look for him, so you’ve walked across the room but, unfortunately, happen to be near his favourite toy. He’s not happy - so growls. You look around, and see RSD. He growled, you looked. That’s ‘attention conspicuity’. In ‘road user’ terms that might be a headlamp, DRL or hi-viz – or tooting your horn to try and get a driver to look at you.

But you may not actually know what a dog is, or how sharp RSD’s teeth might be . . . If you know those things, then you might be more wary of picking up his bone without his permission. And that knowledge, those associations, are cognitive conspicuity – an understanding of the meaning ‘behind’ what you see. Again, in ‘road’ terms, a driver needs to know that ‘single light = motorcycle’, not ‘single light = car far away’, and also that ‘headlamp = person on a bike’. Better still, the driver would have an understanding of a bike’s braking and handling limitations.

This cognitive conspicuity - or lack of - was identified by the trials finding that fewer than half of the participants would expect to see 'people' in the vicinity of vehicles displaying amber beacons.

There is one other aspect to consider here, that of how conspicuity gear can act as camouflage - often known as 'blending'. See the report, top left image in 7-1, and 10-13, to see how the trial was set up for this.

ancient wrote: my understanding that HiViz does not give an increase in safety that would be expected by anyone using 'common sense'.

As the old line goes: the trouble with common sense is that it's not common enough.

[NB See diagram 10-25 for info on the 'colour space' I mentioned earlier]

GTR1400MAN wrote: Well, like the one you mentioned of waiting in a side road to exit

For a motorcyclist, it's the only one I can think of - and I have tried

GTR1400MAN wrote: How about sat a T-junction on an unlit B road waiting to turn and the vehicle is approaching from behind at speed? I'll be seen earlier.

So you have a tail-light, retro-reflective number plate, brake light, your headlamp is illuminating the scene ahead and your indicator is flashing. Plus whatever road signs and markings there are. Will a jacket *really* make any difference?

GTR1400MAN wrote: Or crossing a RAB with a vehicle coming from the left. etc.

Would you rely on chance here? [Also bear in mind you have a sodding great headlamp on the front!] A situation, surely, where if you've identified a potential collision then proactive riding is far more appropriate?

GTR1400MAN wrote: just making me 'bigger' in a head on approach can't be a bad thing.

GTR1400MAN wrote: Load of marketing mumbo jumbo. Not really sure what they are trying to convey.

That they don't know what 'motion' means Well, that may not have been their *aim* - but it's what they achieved! And this also refers back to the 'sign confusion' issue earlier - signs don't move! However, it's been reported in some interviews that workers feel safer when they're stood still next to a big conspicuous vehicle . . .